Quantitative models of sensorimotor systems allow one to combine data from different types of experiments. The advantages of a model include its ability to test the internal consistency of the data and to make predictions which can form the bases for new experiments. A study of the interaction between the visual system and the vestibular system revealed a close coupling between the gradual component of the optokinetic response (OKR) and the gain control of the vestibulo-ocular reflex (VOR). The coupling manifested itself in both linear and nonlinear ways, depending on the measure chosen. This made it impossible to decide whether a single variable gain element, shared by the VOR and the OKR, could explain the results or whether a more complicated arrangement would be required. Existing models of the VOR and OKR were modified to include a single variable gain element, common to both the VOR and the gradual component of the OKR. Simulation of the model on a digital computer reproduced both the linear and nonlinear interactions of the VOR gain change with the OKR.